1. Field of the Invention
The invention relates to a system and a method for controlling an engine, and particularly, to a system and a method for controlling pressure responsive devices that vary compression ratios in engine cylinders.
2. Background Art
A xe2x80x9ccompression ratioxe2x80x9d of an internal combustion engine is defined as the ratio of the volume in a cylinder above a piston when the piston is at bottom-dead-center (BDC) to the volume in the cylinder above the piston when the piston is at top-dead-center(TDC). In general, increasing a compression ratio results in increasing the thermal efficiency of the engine. This in turn results in improved fuel economy and a higher ratio of output energy versus input energy of the engine.
A known variable compression ratio system is disclosed in U.S. Pat. No. 4,834,031 entitled xe2x80x9cVariable Compression-Ratio Control Device For An Internal Combustion Engine.xe2x80x9d The known system utilizes a variable compression ratio (VCR) mechanism for varying a compression ratio of an engine cylinder between a high compression ratio and a low compression ratio. The system applies fluid pressure to the VCR mechanism to switch between a high compression ratio and a low compression ratio and vice versa. However, when the VCR mechanism has a deteriorated response, the system provides no teaching for modifying the stimulus applied to the mechanism to obtain the desired response. For example, when the VCR mechanism is unable to transition an engine cylinder from a low compression ratio to a high compression ratio, the known system merely operates the cylinder at a low compression ratio, regardless of engine operating conditions. Thus, the known system may operate an engine cylinder at the low compression ratio even though a high compression ratio is desired based on engine speed and load, which results in increased fuel consumption and/or increased engine knock.
A system and a method are provided that addresses the problems of the known systems when a pressure responsive device that varies a compression ratio in an engine cylinder has a deteriorated response.
The method for controlling a pressure responsive device in an engine includes supplying fluid pressure to the device to change a compression ratio in an engine cylinder. The pressure responsive device is defined as any device capable of varying a compression ratio in an engine cylinder responsive to a received fluid pressure or pressure signal. For example, a pressure responsive device may include one or more of the following VCR mechanisms: (i) a variable length connecting rod as taught herein, (ii) a variable length connecting rod using an eccentric ring disposed about a crankpin, as disclosed in U.S. Pat. No. 5,562,068, (iii) a variable length connecting rod having a gear arrangement for varying the length of the connecting rod, (iv) a device that can vary a position of an engine cylinder relative to an engine crankshaft, (v) a device that can vary an internal geometry or volume of an engine cylinder, (vi) a device that can vary a piston geometry, such as a piston height or thickness for example, or (vii) a crankshaft having an eccentric crankshaft bearing where the operating position of the bearing is adjusted to vary a cylinder compression ratio.
The method further includes indicating when the device has a deteriorated response. A deteriorated response is defined as any operational response of the device that deviates from a desired or commanded response. For example, a deteriorated response can occur when one or more of the following occur: (i) the device is unable to transition an engine cylinder to a desired compression ratio, or (ii) the device is unable to unable to transition an engine cylinder to the desired compression ratio within a desired time period. Finally, the method includes increasing the fluid pressure to the device to change the compression ratio in the cylinder in response to the indication of deteriorated response.
A system for controlling a pressure responsive device in an engine is provided. The system includes a pressure control device that adjusts a fluid pressure applied to the pressure responsive device based on either a first signal or a second signal. The system further includes a sensor that generates a third signal indicative of a compression ratio of the cylinder. The system further includes a controller operably connected to the pressure control device and the first sensor. The controller is configured to generate the first signal to supply fluid pressure to the pressure responsive device to change a compression ratio in the cylinder. The controller is further configured to determine when the device has a deteriorated response. Finally, the controller is configured to generate the second signal to increase the fluid pressure to the device in response to the indication.
The control system and method for controlling an engine in accordance with the present invention provides a substantial advantage over known systems and methods. In particular, the system and method adjusts the pressure applied to a pressure responsive device, such as a VCR mechanism, when the mechanism has a deteriorated response to obtain a desired compression ratio in an engine cylinder. Thus, the engine may be transitioned to a desired compression ratioxe2x80x94even when the device has a deteriorated responsexe2x80x94which results in increased fuel economy and reduced engine knock.